The monitoring of gases and aerosol concentrations, particularly of lubricating oil mist in working areas of internal combustion engines or in casings of power transmission gears, is of considerable interest for avoiding damages. A rapid increase of the oil mist concentration is indicative of damages, for example of the tearing off of a lubricating film. As a result of frictional heat thus formed, oil vapors are formed which condensate to oil mist in the working area and thus result in a rapid increase of the oil mist concentration. If the resulting hazard is quickly recognized, then explosions and a concomitant threat to persons and further damages to the operating engine can be prevented with appropriate counteractions such as shutting down of the operating engine or of individual components of the operating engine. However, it is also possible to study specific gas components in such a working atmosphere by means of other sensors.
Furthermore, in addition to the tearing off of the lubricating film, so-called blow-throughs may occur between the piston and the associated cylinder wall in bearings of piston engines due to damaged piston rings, which cause a total damage of the piston/cylinder aggregate (“piston seizure”). An increase of the oil mist density with simultaneous rise in temperature due to the hot combustion gases is indicative of such blow-throughs.
First approaches for measuring the oil mist concentration are known from EP-A-0 071 391. In EP-A-0 071 391 it is suggested to draw the aerosol from the working area through a measuring compartment by means of a winged wheel blower and to carry out therein a reflection measurement by means of a radiation source and a radiation sensor. The winged wheel blower suggested therein is intended for use with a plurality of compartments arranged parallel to each other.
The disadvantages of such an arrangement were already shown in WO-A-98/11331. In addition to the considerable constructive and operating expenses of such arrangement, the use of a blower for drawing out has been found to be insufficient, meaning that such a solution should be avoided. Moreover, the drawing out operation also draws dirty air through the pipe system, and thus oil accumulations in the form of oil bags can form which clog the lines, thus rendering the operation of the measuring device difficult or impossible.
In contrast thereto, in DD-A-239 474 and in GB-A-2 166 232 it is suggested to arrange, for each working area of the driving gear of an internal combustion engine, a sensor unit directly in the interior of the respective working area and to connect it via an optical or electrical transmission path to an evaluation unit arranged outside of the internal, combustion engine. However, such a solution is associated with the disadvantage that the base concentration of oil mist and splash oil in the long run contaminates the sensors and, therefore, also leads to false alarms.
In contrast, in the already mentioned WO-A-98/11331 it is suggested to provide, in each working area to be monitored, a sensor unit with an extraction based on a venturi nozzle. Such a measuring device operates without mechanically moving parts and is, therefore, almost wearless. However, it has been found that the air flow generated solely by the crank movement of the crankshaft cannot produce a sufficient perfusion of the vacuum suction nozzle, so that the effectivity of the measuring device is not ensured. In WO 2007/140640 A it was suggested to provide a common external compressed air supply for supplying all of the venturi nozzles of an engine and to ensure supply to the individual measuring points with appropriate supply lines. However, this approach has the disadvantage of requiring complex supply lines.
From DE 26 08 390 A1 it is generally known that a measuring device for indicating the formation of oil mist—and/or oil smoke in engine rooms of internal combustion engines can be configured with an air jet pump, with DE 26 08 390 A1 suggesting to have all of the sampling lines lead into a common collection chamber. But in this manner a differentiated monitoring of the combustion room by means of multiple measuring points, which would allow for localization of the damage site, is not possible.